Thermally stable jet fuel composition

ABSTRACT

Thermally stable turbine or jet fuel composition containing in combination an ethylene-propylene-diene terpolymer/maleic anhydride reaction product and an aldehyde-amine condensation product and a method of operating a turbine engine on said fuel composition.

United States Pate :1

Inventors William M. Sweeney Wappingers Falls;

Kenneth L. Dille, Wappingers Falls; Jerzy J. Bialy, Lagrangeville, all 01 N.Y. 807,942

Mar. 17, l 969 Oct. 26, 197 1 Texaco Inc.

New Yorik, N.Y.

Appl. No. Filed Patented Assignee THERMALLY STABLE JET FUEL COMPOSITION 10 Claims, No Drawings US. Cl 44/62, 44/63, 44/73 lint. Cl Cl0ll/l6,

[50] Field of Search 44/62, 63, 73

[56] References Cited UNITED STATES PATENTS 3,034,876 5/1962 Gee et a1 44/62 3,067,019 12/1962 Churchill et al. 44/62 3,403,011 9/1968 Sweeney 44/62 Primary Examiner-Daniel E. Wyman Assistant Examiner-wi J. Shine Attorneysl(. E. Kavanagh and Thomas H. Whaley ABSTRACT: Thermally stable turbine or jet fuel composition containing in combination an ethylenc-propylene-diene terpolymer/maleic anhydride reaction product and an aldehydeamine condensation product and a method of operating a turbine engine on said fuel composition.

This invention relates to a hydrocarbon fuel composition, specifically a light distillate turbine or jet fuel composition having improved thermal stability and to a method of operating a turbine engine.

It is recognized that petroleum hydrocarbon turbine or jet fuels are susceptible to thermal degradation and oxidation and can produce a suspension of finely divided insoluble bodies in the fuel and cause the formation of deposits on the heatexchanging surfaces. The degree that these undesirable changes take place is dependent on the amount of unstable constituents present in the oil and on the temperature stress and oxidation conditions to which the oil is subjected. The thermal stability rating of fuel compositions of the type in question is determined in Fuel Coker Tests more fully described hereinbelow.

The problem of thermal stability is particularly serious for light hydrocarbon oils which must be maintained at a relatively high temperature for extended periods of time in intimate contact with an oxygen-containing atmosphere. Jet fuels carried in the wing tanks of aircraft are maintained in such an environment. This problem becomes more acute for jet fuel compositions designed to fuel aircraft having speeds in the Mach 2 and 3 speed ranges or above, such as the forthcoming supersonic transports, because of the substantially higher wing tank temperatures which will be generated.

The finely divided insoluble bodies formed in a jet fuel hav ing insufficient thermal stability are separated from the fuel in the fuel filters of the engine. When excessive amounts of insoluble bodies are present in the fuel, the fuel line filters become partially or completely blocked resulting in seriously curtailed or lost engine power due to fuel starvation.

The tendency toward deposit formation in a thermally unstable fuel also causes a deposits buildup on the fuel oil heat exchanger in an airplane known as heater tube deposits. It is recognized that the buildup of heater tube deposits cuts down on the heat-exchanging efficiency and causes lubricating oil overheat and engine failure. In supersonic aircraft, the heat exchanger requirements are further increased because of the need to cool the passenger and crew compartments.

A jet fuel composition has now been discovered having substantially improved thermal stability. More particularly, a jet fuel composition has been discovered which exhibits improved thermal stability even after extended high-temperature stress while under constant agitation in the presence of air. The fuel compositions of this invention are distinguishable from the pour depressed fuel compositions in the commonly assigned US. Pat. No. 3,403,01 l which contain no metal deactivator and do not possess high thermal stability.

In accordance with this invention, there is provided a fuel composition of enhanced thermal stability containing a minor amount of an additive combination comprising an ethylenepropylene-diene terpolymer and maleic anhydride reaction product and a metal deactivator. More particularly, a light hydrocarbon or jet fuel composition is provided containing from about 0.0005 to 0.1 weight percent of the reaction product of a relatively low molecular weight ethylenepropylene-diene terpolymer and maleic anhydride reaction product and from about 0.0003 to 0.0005 weight percent ofa metal deactivator defined below. The method of this invention involves the operation of a jet engine in such a way that the formation of insoluble bodies in the fuel and of heater tube deposits is avoided or minimized.

The ethyIene-propylene-diene terpolymer component of the reaction product additive of this invention consists of polymerized ethylene, propylene, and a C to C nonconjugated diene in the proportions of to 90 mole percent ethylene, 5 to 70 mole percent propylene and 0.1 to mole percent of said diene. This is an amorphous material and has an Inherent Viscosity in the range from 0.2 to 0.9. A preferred composition of this component consists of from 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and l to 5 mole percent diene and is characterized by an Inherent Viscosity in the range of 0.3 to 0.6.

The ethylene-propylene-diene terpolymer reactant employed for preparing the additive of the present invention can be produced by a polymerization reaction followed by a cracking reaction. A mixture of ethylene, propylene and an unconjugated diene in a suitable solvent is polymerized under atmospheric pressure in the presence of a Ziegler-Natta catalyst to produce an amorphous terpolymer product. Suitable unconjugated dienes for the reaction include bi'cyclo (2,2,1) hepta-2,5-diene, l,4-cyclohexadiene, l,5-cyclooctadiene, dicyclopentadiene, diisopropenyl benzene, dipentene, 2,2 dimethyl-l,S-hexadiene, 1,5-heptadiene, 1,5-hexadiene, Z-methyl-l,4-cyclohexadien, methylcyclopentadiene dimer, 5-methylene'2-norbornene, 3-methyl-l,5-heptadiene, 2-methyl-l,5hexadiene, 3-methyl-l,5-hexadiene, 1,7-octadiene, 1,4-pentadiene, 4-vinyl-l-cyclohexene, and Z-methyl- I ,4-pentadiene.

The polymerization reaction is conducted by reacting ethylene, propylene and nonconjugated diene in suitable proportions to produce a polymer consisting of 10 to mole percent ethylene, 5 to 70 mole percent propylene, and 0.1 to 20 mole percent of said diene and having an Inherent Viscosity of at least 1.1. The preferred polymer is one consisting of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and l to 5 mole percent of a nonconjugated diene having from six to 20 carbon atoms and having an Inherent Viscosity in the range of 1.1 to 5. The Inherent Viscosity equals the natural log of the specific viscosity divided by the concentration in grams per ml. The specific viscosity for this equation is the expression of a ratio of the viscosity of the solution divided by the viscosity of the solvent (see Appendix D, pg. I03, Report No. 4 in Polymer Chemistry by Robert McGovern, Stanford Research Institute, Apr. 1965).

The polymer component described must be cracked to a polymer of reduced Inherent Viscosity. This cracking step can be effected by any conventional cracking process but thermal cracking is preferred. It is desirably accomplished by heating the terpolymer to a temperature in the range of 250 to 450 C. and holding the terpolymer in this temperature range until the polymer has been cracked, generally in a period of time ranging from about 15 seconds to 10 hours. The cracked polymer, which is a starting component in the present invention, is characterized by consisting of 10 to 90 percent ethylene, 5 to 70 percent propylene and 0.1 to 20 percent ofa nonconjugated diene having from five to 30 carbon atoms and having an Inherent Viscosity in the range of 0.2 to 0.9.

Alternatively, a suitable low Inherent Viscosity ethylenepropylene-terpolymer can be prepared by polymerizing ethylene, propylene and a nonconjugated diene in the presence of hydrogen and a polymerization catalyst to produce a terpolymer of low Inherent Viscosity.

Maleic anhydride is reacted with a low Inherent Viscosity polymer to produce one additive component of this invention. This reaction is effected by preparing a mixture consisting of about I to 50, preferably from 2 to 15, percent by weight of maleic anhydride and the balance consisting of said terpolymer followed by heating the mixture at a temperature above about 200 C. until the components have reacted. The reaction will generally be completed at a temperature from 200-600 C. in a period of time ranging from about 30 minutes to 12 hours although shorter and longer reaction periods can be employed. The ethylene-propylene-diene terpolymer and maleic anhydride are conveniently reacted in a mineral oil carrier to produce an oil solution of the reaction product followed by vacuum stripping of any unreacted material from the oil solution.

The above reaction product is generally employed in the fuel composition in a concentration ranging from about 0.0005 to 0.1 weight percent with the preferred concentration of this additive being in the range of 0.001 to 0.005 weight percent, the latter amounts corresponding to about 3 and I5 p.t.b. (pounds per thousand barrels).

The metal deactivator component of this invention is an aldehyde-amine condensation product represented by the formula:

in which R is a divalent hydrocarbyl radical having from two to four carbon atoms. Examples of typical deactivators are N,N'-disalicyclidene-and N,Ndisalicyclidene- 1 ,2- ethanediamine. The metal deactivator is employed in the fuel at a concentration ranging from about 0.0003 to 0.005 weight percent which corresponds to about 0.8 and 14 p.t.b. respectively.

EXAMPLE I 100 grams of a commercial mixture consisting of two parts by weight of an ethylene-propylene-hexadiene terpolymer consisting of approximately 65 mole percent ethylene, 34 mole percent propylene and 1 mole percent 1,4-hexadiene having an Inherent Viscosity of 2.10 and one part heavy naphthenic oil was comminuted and admixed with 100 grams of a refined paraffinic mineral oil having an API Gravity of 34 and an SSU Viscosity of 39 at 210 F. This mixture was heated for 5 minutes at 350 C. to crack the terpolymer and disperse it throughout the oil. The oil mixture of cracked terpolymer was cooled to 250 C. and 5 grams of maleic anhydride added.

This mixture was then reacted under agitation at 250 C. for 7 hours. The resultant reaction product oil mixture was stripped of unreacted maleic anhydride by heating under a vacuum at 250 C. for 2 hours. The resultant oil solution contained 43 percent of the reaction product as determined by dialysis and this reaction product had an Inherent Viscosity of 0.56 as determined in toluene at 100 F.

EXAMPLE II 100 grams of an ethylene-propylene-dicyclopentadiene terpolymer consisting of about 62 mole percent ethylene, 37 mole percent propylene and 1 mole percent dicyclopentadiene in a heavy napththenic oil (50-50) was comminuted and mixed with an equal weight of the refined paraffmic lubricating oil of example 1. This mixture was heated to 350 C. for about 5 minutes to effect cracking of the terpolymer and dispersion in the oil. The resultant mixture was cooled to about 250 C., 2.5 grams of maleic anhydride added, and the mixture reacted for 1 hour at 250 C. Unreacted maleic anhydride was removed by heating under vacuum at 250 C. for an hour. The reaction product contained 21 percent of the terpolymer by dialysis and had an Inherent Viscosity of0.68.

EXAMPLE III 100 grams of an ethylene-propylene-dicyclopentadiene terpolymer consisting of 62 mole percent ethylene, 37 mole percent propylene and 1 mole percent dicyclopentadiene in a heavy naphthenic oil (5050) and 400 grams of the light refined paraffinic oil of example I were heated to 350 C. for 5 minutes and then cooled. 5 grams of maleic anhydride were added and the mixture reacted at 250 C. for 7.5 hours. The reaction mixture was vacuum stripped of unreacted maleic anhydride by heating at 250 C. over a 2-hour period. The oil mixture contained 10 percent of the terpolymer-maleic anhydride reaction product by dialysis and had an Iodine Number of 7.85. Infrared spectra of the product showed the presence of anhydride groups. The reaction product has an Inherent Viscosity of 1.98 measured in toluene at 100 F.

EXAMPLE IV A gasmixture of 40 p.s.i.g. ethylene, 80 p.s.i.g. propylene and 10 p.s.i.g. hydrogen was used to saturate 2 liters of heptane at 60 F. 2 ml. of dicyclopentadiene was added to the saturated heptane solution. An additional quantity of the gas mixture was passed through the heptane solution while 8 ml. of a 20 percent diethylaluminum chloride solution in n-heptane and 2 ml. ofa 20 percent solution of tri-n-butyl vanadate in n-heptane were added over a period of 20 minutes. The reaction product was treated with 250 ml. of percent hydrochloric acid at 178 F. for 1.5 hours resulting in the separation of an aqueous layer. The volume of the heptane layer was reduced by one-half its volume by evaporation over a steam plate. About 50 grams of cetane and 0.1 grams of an- 0 tioxidant 2,6-di-t-butyl-4-methyl phenol were added and the mixture stripped to 500 F. under a slight vacuum. The reactant product weighed 76 grams and was calculated to contain 26 grams of terpolymer.

About 1.28 grams of maleic anhydride was added to the mixture and the mixture reacted with stirring at 250 C. under a nitrogen atmosphere for 7 hours. The product was then vacuum stripped of unreacted maleic anhydride at 250 C. for 1 hour. 70.1 grams of product were recovered containing 35 percent terpolymer by dialysis. The product had an Iodine Number of 3.0 and infrared spectra showed typical spectra for ethylene-propylene-dicyclopentadiene terpolymer with peaks associated with anhydride groupings. The ethylene-propylene ratio of the terpolymer by NMR was 1.7-1 and the Inherent Viscosity of the polymer-anhydride reaction product in toluene was 0.6 at F.

The preparation of the turbine or jet fuel composition of the invention simply involves the addition of the two-component additive to the fuel in the indicated amounts.

The effectiveness of the fuel compositions of the invention was determined by preparing typical jet fuel compositions and testing for thermal stability in Fuel Coker Tests. The standard Fuel Coker Test employed to test the thermal stability of jet fuels is the CFR Fuel Coker Test (ASTM-D-l 660-61-T.

The fuels being formulated for use in supersonic flight are so thermally stable that the conditions of the standard CFR Fuel Coker Test do not approach or test the thermal stability limits of these fuels. Because of this, a much more severe test has been developed called the CFR Research Fuel Coker Test. This test is patterned after the standard CFR Fuel Coker Test and uses similar equipment manufactured by the Erdco Engineering Corporation who make all of the industry-adopted Fuel Coker Test equipment. The principal difference in the Research Fuel Coker Test is that the fuel is maintained at an elevated temperature, usually 200 F. for an extended period of time, generally 5 hours, all the while being agitated or stirred in the presence of air. This treatment markedly increases the thermal stress placed on the fuel composition. The balance of the test is similar to the standard CFR Fuel Coker Test in that the fuel ispassed over a heated tube for the determination of tube deposits (tube rating) and through a heated filter to measure filter plugging. The Research Fuel Coker Test is described in Technical Documentary Report No. ASD-TDR2852, Sept. 1962 of the US. Air Force under the subject An Investigation of the Thermal Stability of Potential Supersonic Jet Fuels."

The conditions under which the coking tests are conducted follow the procedure set forth in the CFR Fuel Coker Test wherein the severity of the temperature of the heater tube and fuel filter are increased in 25 F. increments until the fuel fails to pass the test. These temperatures are important indicators of the severity of the test and are shown in the test results. The fuel flow employed is a rate of 6 lbs. per hour for 5 hours (300 minutes). When and if the back pressure caused by filter plugging reaches 25.0 inches of mercury before 300 minutes, the fuel fails this test but the run is continued with the filter bypassed until the 300 minutes elapse. For military purposes, a filter pressure of less than 12.0 inches of mercury in 300 minutes is satisfactory according to M1LJ-5624F. The deposits formed on the tube are rated as from 0=best to 4=worst in the CFR Fuel Coker Test and from 0=best to 8=worst in the Research Coker Test. In either test, a tube rating of 2 or less passes and a rating of 3 or more fails the tube rating test.

Run illustrates the present invention. This fuel composition is the only fuel composition to pass the preheater and filter ratings in the Research Coker thermal stability test.

The present invention represents a remarkable improve- 5 ment in the develo ment of turbine and 'et fuels which exhibit p 4 J a high level of thermal stability under conditions of high tem- Gmh AH 43 5 perature stress. ASTMybismlamm,0Fv Obviously, many modifications and variations of the inven tion, as hereinbefore set forth, may be made without departing mp 327 10 from the spirit and scope thereof, and therefore, only such I0 limitations should be imposed as are indicated in the ap- 20 374 pended claims. :8 404 We claim: 1. A jet fuel composition comprising a major proportion ofa 43s 15 light distillate mineral oil and minor amounts of: 1. an aldeh de-amine condensation roduct re resented by 30 457 y P p 487 the formula: 502 EP 517 (HI 0H 20 H H Flash Point, F. I25 Freezing Point, F. -56 FlA Analysis Aromatics 75 13.5 Olcfins 2.0 25 in which R is a divalent hydrocarbyl radical having from two Net Heat of Combustion Emu/L 18 483 to four carbon atoms, and Luminomctcr Number 514 2. an additive comprising the reaction product of maleic anhydride and an ethylene-propylene-diene terpolymer 30 prepared by forming a mixture of from I to 50 percent maleic anhydride and the balance said ethylene propylene-diene terpolymer and heating said mixture The effectiveness of the additives of the invention in the above about 200 C. until the reaction has been substanabove jet fuel is shown by the Fuel Coker TEst results set forth tially completed, said ethylene-propylene-diene terin the tables below. The concentration of the additive com- 35 polymer consisting of ethylene, propylene and a noncon ponents in the fuels is shown in p.t.b. (pounds per thousand jugated diene having from five to 30 carbon atoms, in the barrels) of the fuel composition. The concentration of the mole ratios of from 10 to 90 mole percent ethylene, 5 to polymer is shown on the active material basis (minus the 70 mole er nt propylene and 0.] to 20 mole percent f diluent oil). said diene, said ethylene-propylone-diene terpolymer 40 TABLE I.-ASTM (JOKER THERMAL STABILITY TEST Rating Metal Filter Polymer deac- Temperature cone. tlvator of preheater/ A 1, Time Run Fuels (PTB) (PTB) filter Preheater Hg niln 300/400 1 O. '2 300 2 400/500 [4 0 300 4 .35 3 450 550 14 166 4 3 450/550 3 35 105 5. 3 450/550 .3 0 300 0 450/550 4 0 300 7. 3 3 450/550 1 0. 3 300 8. do 7 450/550 4 0. 3 300 9 xample IV 7 3 450/550 l 0. 7 300 10 Example III. 7 450/550 4 0. 9 300 l N, N-disalicylidene-1, Z-propanediamine.

Runs 5, 7 and 9 in the above table are illustrative of the present invention. At the highest severity level, namely preheater and filter temperature levels of 450/550 F., the fuel compositions of Runs 5, 7 and 9 are the only fuels which pass both the preheater and filter ratings.

TABLE IL-RESEARCH (JOKER THERMAL STA being amorphous and having an Inherent Viscosity in the range of0.2 to 0.9.

2. A fuel composition according to claim 1 in which said condensation product is N ,N-disalicylidenel ,2-

propanediamine and said terpolymer consists of ethylene,

BILITY TEST Rating Metal Temperature Filter Polymer deacof reservoir cone. tlvator preheater/ A P, 'Ilme. Run Fuels (PTB) (PTB) lter Preheater Hg min.

u N, N-disalicy1idene-1, 2-propanedlamine.

7 propylene and l,4-heitadiene 3. A fuel composition according to claim 1 in which said condensation product is N,N -disalicylidenel ,2- propanediamine and said terpolymer consists of ethylene, propylene and dicyclopentadiene.

4. A fuel composition according to claim 1 containing from about 0.0003 to 0.005 weight percent of said condensation product and from about 0.0005 to 0.1 weight percent of said reaction product.

5. A fuel composition according to claim 1 in which said terpolymer consists of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and l to 5 mole percent of a nonconjugated diene.

6. A fuel composition according to claim 1 in which said terpolymer consists of about 65 mole percent ethylene, about 34 mole percent propylene and about 1 mole percent 1,4-hexadiene.

7. A fuel composition according to claim 1 in which said terpolymer consists of about 62 mole percent ethylene, about 37 mole percent propylene and about 1 mole percent of dicyclopentadiene.

8. A method for operating a turbine engine which comprises supplying to and burning in said engine a jet fuel composition comprising a major proportion of a light distillate mineral oil containing 1. 0.0003 to 0.005 weight percent of an aldehyde-amine condensation product represented by the formula:

in which R is a divalent hydrocarbyl radical having from two to four carbon atoms, and

2. 0.0005 to 0.1 weight percent of a reaction product of maleic anhydride and an ethylene-propy1ene-diene terpolymer prepared by forming a mixture of from 1 to 50 percent maleic anhydride and the balance said terpolymer and heating said mixture above about 200 C. until said reaction has been substantially completed, said ethylene-propylene-diene terpolymer consisting of ethylene, propylene and a nonconjugated diene having from five to 30 carbon atoms, in the mole ratios of from 10 to mole percent ethylene, 5 to 70 mole percent propylene and 0.1 to 20 mole percent of said diene, said terpolymer being amorphous and having an Inherent Viscosity in the range of0.2 to 0.9.

9. A method according to claim 8 in which said condensation product is N,N'-disalicylidene-1,2-propanediene and said terpolymer consists of ethylene, propylene and 1,4-hexadiene.

10. A method according to claim 8 in which said condensation product is N,N'-disalicylidene-l,2-propanediamine and said terpolymer consists of ethylene, propylene and dicyclopentadiene. 

2. an additive comprising the reaction product of maleic anhydride and an ethylene-propylene-diene terpolymer prepared by forming a mixture of from 1 to 50 percent maleic anhydride and the balance said ethylene-propylene-diene terpolymer and heating said mixture above about 200* C. until the reaction has been substantially completed, said ethylene-propylene-diene terpolymer consisting of ethylene, propylene and a nonconjugated diene having from five to 30 carbon atoms, in the mole ratios of from 10 to 90 mole percent ethylene, 5 to 70 mole percent propylene and 0.1 to 20 mole percent of said diene, said ethylene-propylene-diene terpolymer being amorphous and having an Inherent Viscosity in the range of 0.2 to 0.9.
 2. A fuel composition according to claim 1 in which said condensation product is N,N''-disalicylidene-1,2-propanediamine and said terpolymer consists of ethylene, propylene and 1,4-hexadiene.
 2. 0.0005 to 0.1 weight percent of a reaction product of maleic anhydride and an ethylene-propylene-diene terpolymer prepared by forming a mixture of from 1 to 50 percent maleic anhydride and the balance said terpolymer and heating said mixture above about 200* C. until said reactioN has been substantially completed, said ethylene-propylene-diene terpolymer consisting of ethylene, propylene and a nonconjugated diene having from five to 30 carbon atoms, in the mole ratios of from 10 to 90 mole percent ethylene, 5 to 70 mole percent propylene and 0.1 to 20 mole percent of said diene, said terpolymer being amorphous and having an Inherent Viscosity in the range of 0.2 to 0.9.
 3. A fuel composition according to claim 1 in which said condensation product is N,N''-disalicylidene-1,2-propanediamine and said terpolymer consists of ethylene, propylene and dicyclopentadiene.
 4. A fuel composition according to claim 1 containing from about 0.0003 to 0.005 weight percent of said condensation product and from about 0.0005 to 0.1 weight percent of said reaction product.
 5. A fuel composition according to claim 1 in which said terpolymer consists of 50 to 90 mole percent ethylene, 5 to 45 mole percent propylene and 1 to 5 mole percent of a nonconjugated diene.
 6. A fuel composition according to claim 1 in which said terpolymer consists of about 65 mole percent ethylene, about 34 mole percent propylene and about 1 mole percent 1,4-hexadiene.
 7. A fuel composition according to claim 1 in which said terpolymer consists of about 62 mole percent ethylene, about 37 mole percent propylene and about 1 mole percent of dicyclopentadiene.
 8. A method for operating a turbine engine which comprises supplying to and burning in said engine a jet fuel composition comprising a major proportion of a light distillate mineral oil containing
 9. A method according to claim 8 in which said condensation product is N,N''-disalicylidene-1,2-propanediene and said terpolymer consists of ethylene, propylene and 1,4-hexadiene.
 10. A method according to claim 8 in which said condensation product is N,N''-disalicylidene-1,2-propanediamine and said terpolymer consists of ethylene, propylene and dicyclopentadiene. 